The present invention relates in general to rotatable heat exchangers, sometimes known as heat recovery wheels, and in particular, it relates to a novel mounting structure for such heat recovery wheels. In gas turbines, furnaces, and other combustion chambers, it is desirable to preheat incoming combustion gases with heat extracted from exhaust gases, thereby increasing combustion efficiency. Rotary heat exchangers or heat recovery wheels are particularly desirable for this purpose. Heat recovery wheels are generally mounted for rotation about a central axis. The wheel first rotates through the exhaust gas stream. The wheel has apertures extending therethrough in the axial direction and as gases flow through the apertures, heat is extracted from the exhaust gas stream and absorbed by the wheel. As the wheel further rotates through the incoming gas stream, this heat is given up by the wheel to the incoming gas.
While heat recovery wheels may be made from metal, ceramic materials are preferred because ceramic materials have a low coefficient of thermal expansion and a high resistance to oxidation and corrosion. However, even though ceramics are chosen for the body of such wheels, metals are still employed for the hub driver therefor. Since the coefficient of expansion of the metal hub differs from the coefficient of expansion of the ceramic, it is generally necessary to securely mount the wheel to the hub while permitting differential thermal expansion of the hub in the axial and radial directions with respect to the wheel.
The mounting of such metal hubs to ceramic heat recovery wheels has posed somewhat of a problem to the prior art. Since rigid connections cannot be made between the metal hub and the ceramic rotary heat recovery wheel, slippage may at times occur between the ceramic wheel and the metal hub. Such slippage is detrimental since the ceramic disk may thus be subjected to unwanted temperature variations across its diameter. Such temperature variations may cause cracking and breakage of the ceramic disk.
It would be desirable to provide an improved rotary heat recovery wheel having a mounting device therefor which prevents slippage between the ceramic disk and metal hub thereof.